Catheter having multiple-needle electrode and methods thereof

ABSTRACT

An improved ablation catheter with at least one multiple-needle electrode can be used in ablating the arrhythmogenic region instead of an arrhythmogenic point of a patient. This catheter is particularly useful for treating the patient with atrial fibrillation (AFib) indications. A catheter suitable for radiofrequency ablation of cardiac tissues comprises a delivery catheter and an inner catheter having a distal section, a distal end, a proximal end and at least one lumen extending therebetween. The ablation catheter has a temperature sensor and a close-loop temperature control. The steerable catheter having at least one multiple-needle electrode is inserted into the chambers of the heart to create a plurality of deep, large, and contiguous lesions by applying radiofrequency energy to said electrode.

FIELD OF THE INVENTION

The present invention generally relates to improved constructions for acardiovascular catheter. More particularly, this invention relates toapparatus and methods for ablating cardiac arrhythmias via a steerableablation catheter having at least one multiple-needle electrode forablating intracardiac tissues resulting in a plurality of deeper andlarger lesions in the myocardium or epicardium of the heart.

BACKGROUND OF THE INVENTION

Symptoms of abnormal heart rhythms are generally referred to as cardiacarrhythmias, with an abnormally rapid rhythm being referred to as atachycardia. The present invention is concerned with the treatment oftachycardias which are frequently caused by the presence of an"arrhythmogenic site" or "accessory atrioventricular pathway" close tothe inner surface of the chambers of a heart. The heart includes anumber of normal pathways which are responsible for the propagation ofelectrical signals from upper to lower chamber necessary for performingnormal systole and diastole function. The presence of arrhythmogenicsite or accessory pathway can bypass or short circuit the normalpathway, potentially resulting in very rapid heart contractions,referred to here as tachycardias.

Treatment of tachycardias may be accomplished by a variety ofapproaches, including drugs, surgery, implantablepacemakers/defibrillators, and catheter ablation. While drugs may be thetreatment of choice for many patients, they only mask the symptoms anddo not cure the underlying causes. Implantable devices only correct thearrhythmia after it occurs. Surgical and catheter-based treatments, incontrast, will actually cure the problem, usually by ablating theabnormal arrhythmogenic tissue or accessory pathway responsible for thetachycardia. It is important for a physician to accurately steer thecatheter to the exact site for ablation. Once at the site, it isimportant for a physician to control the emission of energy to ablatethe tissue within the heart.

Of particular interest to the present invention are radiofrequency (RF)ablation protocols which have proven to be highly effective intachycardia treatment while exposing a patient to minimal side effectsand risks. Radiofrequency catheter ablation is generally performed afterconducting an initial mapping study where the locations of thearrhythmogenic site and/or accessory pathway are determined. After amapping study, an ablation catheter is usually introduced to the targetheart chamber and is manipulated so that the ablation tip electrode liesexactly at the target tissue site. Radiofrequency energy or othersuitable energy is then applied through the tip electrode to the cardiactissue in order to ablate the tissue of arrhythmogenic site or theaccessory pathway. By successfully destroying that tissue, the abnormalsignal patterns responsible for the tachycardia may be eliminated.However, in the case of atrial fibrillation (AFib), multiplearrhythmogenic sites and/or multiple accessory pathways exist. Theconventional catheter with a single ablation tip electrode can noteffectively cure the symptoms.

Atrial fibrillation is believed to be the result of the simultaneousoccurrence of multiple wavelets of functional re-entry of electricalimpulses within the atria, resulting in a condition in which thetransmission of electrical activity becomes so disorganized that theatria contracts irregularly. Once considered a benign disorder, AFib nowis widely recognized as the cause of significant morbidity andmortality. The most dangerous outcome from AFib is thromboembolism andstroke risk, the latter due to the chaotic contractions of the atriacausing blood to pool. This in turn can lead to clot formation and thepotential for an embolic stroke. According to data from the AmericanHeart Association, about 75,000 strokes per year are AFib-related.

A catheter utilized in the radiofrequency ablation is inserted into amajor vein or artery, usually in the neck or groin area. The tip sectionof a catheter is referred to here as the portion of that catheter shaftcontaining the electrode or electrodes which may be deflectable. Thecatheter is then guided into the appropriate chamber of the heart byappropriate manipulation through the vein or artery. The tip of acatheter must be manipulatable by a physician from the proximal end ofthe catheter, so that the electrode at the tip section can be positionedagainst the tissue site to be ablated. The catheter must have a greatdeal of flexibility in order to follow the pathway of major bloodvessels into the heart. It must permit user manipulation of the tip evenwhen the catheter body is in a curved and twisted configuration. The tipsection of a conventional electrophysiology catheter that is deflectableusually contains one large electrode about 4 mm in length for ablationpurpose. The lesion is generally not deep because of a flat contactsurface.

After the exact location of a target tissue is identified, the ablationapparatus may still not easily approach the target site even withassistance of an internal viewing means, such as an endoscope. Thisviewing situation may turn into a nightmare when an endoscope approachbecomes prohibitive or unavailable during procedures. An externalultrasonic imaging capability therefore becomes in need so that ablationis not taking place in an inappropriate location. In the U.S. Pat. No.4,794,931, there has been disclosed a catheter apparatus and systemwhich can be utilized for ultrasonic imaging. However, there is nodisclosure to how such an apparatus and system can be utilized inconjunction with a endocardial ablation apparatus having multiple-needleelectrodes to achieve the desired ultrasonic imaging and ultimately thedesired ablation.

Imran in U.S. Pat. No. 5,281,218 teaches a needle electrode attached ona catheter for radiofrequency ablation. Though a needle like electrodeis beneficial to ablate a tissue point for deep lesion, it is notpossible to make a plurality of deeper and larger lesions in a regionsuch as in the case of atrial fibrillation or in the case of epicardialside of the myocardium. For atrial fibrillation treatment, thelimitation of said technique is obvious because of its single ablationpoint.

While a radiofrequency electrophysiology ablation procedure using anexisting catheter has had promising results, the tip section of a knowncatheter usually have only one large electrode or one needle electrodefor ablation purpose. Therefore there is a need for a new and improvedcatheter for making a plurality of deeper and larger lesions in themyocardium or epicardium of the heart.

SUMMARY OF THE INVENTION

In general, it is an object of the present invention to provide animproved ablation catheter with at least one multiple-needle electrodewhich can be used in ablating the arrhythmogenic region instead of anarrhythmogenic point of a patient. This catheter is particularly usefulfor treating the patient with atrial fibrillation (AFib) indications. Inone embodiment, an ablation catheter comprises a delivery catheterhaving a distal end, a proximal end and at least one lumen extendingtherebetween. A handle is attached to the proximal end of said deliverycatheter.

The delivery catheter has an electrode deployment means. The electrodedeployment means includes a retractable inner catheter having a tipsection, comprising at least one multiple-needle electrode. The innercatheter comprises a distal end, a proximal end, and a central lumenextending therebetween. The proximal end is attached to the electrodedeployment means which has a push-pull type mechanism on the handle. Inone embodiment, the multiple-needle electrode becomes the tip electrodewhile a plurality of band electrodes spaced at a pre-determined distancefrom the preceding electrode. In an alternate embodiment, themultiple-needle electrode contains a plurality of needles on saidelectrode. In a further embodiment, the plurality of needles on at leastone electrode faces outward toward the tissue surface to be ablated.Therefore, at ablation time, the needles are positioned essentiallyperpendicular to the tissues to be ablated. In still another embodiment,the needles face at different directions so as to contact theendocardial tissue when a bi-directional deflectable catheter is used inthe ablation procedure. The inner catheter has a non-deployed state whenit is positioned in the delivery catheter. This non-deployed state ismaintained during the ablation catheter insertion operation into apatient and during withdrawal of the catheter from a patient.

The ablation catheter further comprises a steering mechanism at thehandle for controlling the deflection of said multiple-needle electrode.Usually a rotating ring or a push-pull plunger is employed in thesteering mechanism. In another embodiment, the steerable ablationcatheter comprises a bi-directional deflection of the tip section havingat least one multiple-needle electrode. One end of the steering wire isattached at certain point of the tip section of said inner catheter. Theother end is attached to the steering mechanism at the handle. Thesteering mechanism on a steerable catheter or device is well-known tothose who are skilled in the art.

The inner catheter has a deployed state when it is advanced out of thedistal end of said delivery catheter. Deployment of the inner catheteris accomplished by a pushing action on the push-pull deploymentmechanism at the handle. In one embodiment, the tip section of thedeployed inner catheter has a preformed shape so that the electrode ofthe multiple-needle electrodes would extend outwardly of the deliverycatheter when deployed. The degree of deployment is controlled by thepushing action at said push-pull mechanism on the handle and isproportional to the push distance on the push-pull plunger of thepush-pull mechanism which is quantifiable.

The deployed inner catheter having at least one multiple-needleelectrode, defines an ablation target. The sharp point of the needles ofeach electrode is positioned at the forward side facing the targettissue. After finishing the ablation operation, the retraction of theinner catheter is accomplished by pulling back the inner catheterrelative to the delivery catheter. The degree of retraction is mainlycontrolled by the pulling action at the push-pull mechanism on thehandle.

At least one conducting wire which is soldered to the electrode passesthrough the lumen of the inner catheter and the interior void of thehandle and is thereafter soldered to a contact pin of the connectorsecured at the proximal end of the handle. Therefrom, the conductingwire is connected to an external RF generator for ablation operationsand/or to an EKG monitor for recording and display of the endocardialelectrical signal.

In an additional embodiment, the ablation system further comprises atemperature sensing and close-loop temperature control mechanism for theelectrode having at least one temperature sensor at the tissue contactsite of the electrodes. The location of the temperature sensor ispreferably in the proximity of one of the needles of the electrodes.

In a particular embodiment, the length of an additional multiple-needleelectrode is 4 mm or longer. In an alternate embodiment, the needles onan electrode are equally spaced and the distance between the needle tipof an additional multiple-needle electrode is 2 mm or less. The heightof the needle is usually 1 mm or less. The material for themultiple-needle electrode may consist of conductive metals such asplatinum, iridium, gold, silver, stainless steel, Nitinol, or an alloyof their mixture.

In a still further embodiment, the tip section of the inner cathetercomprising the electrodes is formed of a conducting material withoutcatheter shaft. The multiple-needle electrode in this embodiment isformed of a flexible metal mesh that can be retracted into the deliverycatheter during inserting and withdrawal of said inner catheter system.

In order to provide increased torsional rigidity to the catheter shaft,the shaft material preferably comprises a polymeric tube having aDurometer in the range from 30 D to 90 D, usually from 40 D to 65 D.Preferably, the shaft has a composite structure including a base layerof a relatively low Durometer material, a stiffening layer, for example,metal braid or coil, and an outer layer comprising the biocompatiblepolymeric material or the material that may render itself biocompatibleby surface treatment. To enhance biocompatibility, the catheter shaftfurther comprises surface coating of heparin on the surface of thecatheter shaft. It is hypothesized that the coated heparin forms abarrier, while not releasing heparin from said surface, between theblood and the catheter surface to enhance biocompatibility duringelectrophysiology procedures. In a further embodiment, an ablationcatheter further comprises surface treatment of low surface energysubstrates, such as Teflon® type fluorinated polymers, to mitigate bloodcoagulation during high energy ablation. Fluorinated polymer can bedeposited on the shaft surface via plasma coating technology or thelike.

A method for operating a steerable ablation catheter system having atleast one multiple-needle electrode at the tip section of an deployableinner catheter within a heart chamber comprises percutaneouslyintroducing the delivery catheter through a blood vessel to the heartchamber, wherein the multiple-needle electrode is deployed by pushingthe inner catheter forward and forming the desired electrode pre-shape;deflecting the distal section of the inner catheter about a transverseaxis to position the multiple-needle electrode near a target region onan interior wall of the heart chamber; intimately contacting theelectrode, including the needles, with the intracardiac tissue; andapplying radiofrequency energy to the target location through theneedles of this invention.

Another object of the invention is to provide a catheter and methods inwhich it is possible to view the area to be ablated prior to ablation toensure that ablation is being carried out in an appropriate location.The electrode having a plurality of needles is encoded with plurality ofmarkers which are visible to ultrasonic energy. The markers have beenprovided in the form of encapsulated air bubbles. In another embodiment,probes with ultrasonic signal capability are located adjacent to theneedle of said electrode. The ultrasonic signals are directed outwardlyand received inwardly relative to the front side of the electrode topermit rapid and substantially continuous viewing of the target tissue.

The method and apparatus of the present invention have severalsignificant advantages over known catheter or ablation techniques. Inparticular, the multiple-needle electrode of a steerable ablationcatheter of this invention may result in a plurality of deeper, largerand contiguous lesions which is highly desirable in the AFib treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and features of the present invention will becomemore apparent and the invention itself will be best understood from thefollowing Detailed Description of the Exemplary Embodiments, when readwith reference to the accompanying drawings.

FIG. 1 is an overall view of a catheter having at least onemultiple-needle electrode constructed in accordance with the principlesof the present invention.

FIG. 2 is a close-up view of the distal section of the catheter atnon-deployed state.

FIG. 3 is a cross-sectional view of the tip section of the innercatheter having multiple-needle electrodes.

FIG. 4 is a perspective view of the tip section of the inner catheter ofFIG. 1.

FIG. 5 shows the contact of the multiple-needle electrode of thecatheter of this invention with the tissue.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a perspective view of the catheter having a deliverycatheter. An ablation catheter constructed in accordance with theprinciples of the present invention comprises: a delivery catheter 1having a distal end 7, a proximal end 10, and at least one lumentherebetween. The delivery catheter comprises an electrode deploymentmeans, wherein the deployment means comprises a retractable innercatheter 2 having a tip section, comprising at least one multiple-needleelectrode. A handle 4 is attached to the proximal end 10 of saiddelivery catheter 1.

The connector 3 secured at the proximal end of the catheter is part ofthe handle section 4. The handle has one steering mechanism 5 and oneinner catheter deployment mechanism 6. The steering mechanism 5 is todeflect the tip section of the inner catheter 2 when the tip section isdeployed outside of the distal end 7 of said delivery catheter 1. Bypushing the front plunger 8 of the handle 4, the tip section of theinner catheter deflects to one direction. By pulling the front plunger8, the tip section returns to its neutral position.

The deployment mechanism 6 constitutes a catheter shaft for the innercatheter, wherein the catheter shaft resists buckling inside thedelivery catheter 1 and inside the cavity of the handle 4. The rearplunger 9 is used to push the tip section of the inner catheter 2outwards of the delivery catheter 1 for ablation purpose. While thecatheter is introduced into the body or removed from the body, the tipsection of the inner catheter 2 is retracted into the delivery catheter1 by pulling back the rear plunger 9.

FIG. 2 shows a close-up view of the distal section of the catheter atnon-deployed state of FIG. 1. The tip section of the delivery cathetercomprises a distal end 7 and a sealable opening 11. The tip section ofthe inner catheter 2 comprises a tip electrode 12 which has a pluralityof needles 13, and at least one band electrode 14 which has a pluralityof needles 15. The electrodes are formed of a conducting material. Inone embodiment, at least one electrode is a metal mesh securely wrappedoutside of the catheter shaft of the inner catheter 2, wherein theelectrode has a plurality of needles 14 or 15.

FIG. 3 shows a cross-sectional view of the tip section with at least onetemperature sensor 17 and ultrasonic imaging capabilities. In order toenhance the ablation positioning of said ablation catheter, theelectrode is encoded with markers 19 which are visible to ultrasonicenergy. Such markers 19 are provided in the form of encapsulated airbubbles. Several markers 19 are placed on the same side of the needlesand in the proximity of the needles 15 of the multiple-needle electrode14 in a way so that the exact location of the needles 15 is visible toan external ultrasonic energy. By way of example, the bubble in a markercan be formed by introducing air by a syringe (not shown) penetratingthe wall of the plastic front body of said electrode and thereafter issealed by epoxy.

The multiple-needle electrode has an insulated conducting wire 16 whichpasses through the lumen of the inner catheter 2 and is soldered to acontact pin of the connector 3 at the proximal end of the handle 4. Theconducting wire from the connector end is externally connected to an EKGfor diagnosis or to an RF generator during an electrophysiology ablationprocedure. Therefrom, the RF energy is transmitted through theconducting wire to the multiple-needle electrode and delivered theenergy to the target tissue.

A temperature sensor 17, either a thermocouple or a thermister, isconstructed at the proximity of one needle 13 or 15 of the electrodes 12or 14 to measure the tissue contact temperature when RF energy isdelivered. The temperature sensing wire 18 from the thermocouple orthermister is connected to one of the contact pins (not shown) of theconnector 3 and externally connected to a transducer and to atemperature controller. The temperature reading is thereafter relayed toa close-loop control mechanism to adjust the RF energy output. The RFenergy delivered is thus controlled by the temperature sensor reading orby the pre-programmed control mechanism.

The tip section having at least one multiple-needle electrode formed ofconducting material can be extended out of the delivery catheter 1 andretracted into said delivery catheter by a deployment mechanism 6 at thehandle 4. To prevent blood from backflow into the delivery catheter 1, asilicone type sealer 11 is installed at certain opening of the deliverycatheter between the delivery catheter 1 and the inner catheter 2.

FIG. 4 shows a perspective view of the tip section of the innercatheter, wherein the tip section comprises a plurality of electrodeshaving a plurality of needles secured onto the electrode. For thesteering mechanism 5, a steering wire is firmly attached onto a flatwire or coil spring (not shown) at the distal contact point of said flatwire. The proximal end of the steering wire is secured to the push-pullplunger 8 of the steering mechanism. By pushing or pulling the steeringwire from the handle, the distal portion of the inner catheter 2deflects to one direction.

FIG. 5 shows the contact of the needles 13 and 15 of the multiple-needleelectrodes 12 and 14 with the target tissue 20. The needle may contactthe tissue at an angle essentially perpendicular to the target tissue.RF energy is applied thereafter and a plurality of deep and largelesions are created which are contiguous for the treatment of atachycardia.

From the foregoing, it should now be appreciated that an improvedablation catheter having multiple-needle electrode and a steerablemechanism has been disclosed for ablation procedures, includingendocardial and body tissue ablations. While the invention has beendescribed with reference to a specific embodiment, the description isillustrative of the invention and is not to be construed as limiting theinvention. Various modifications and applications may occur to thoseskilled in the art without departing from the true spirit and scope ofthe invention as described by the appended claims.

What is claimed is:
 1. A method for operating a steerable ablationcatheter within a heart chamber, the steerable ablation catheter havinga deployable inner catheter and having an additional multiple-needleelectrode at the tip section of the inner catheter, wherein themultiple-needle electrode has a longitudinal length of 4 mm orlonger;the method comprising the steps of: (a) percutaneouslyintroducing the steerable ablation catheter through a blood vessel tothe heart chamber, wherein the multiple-needle electrode is deployed byadvancing the inner catheter forward; (b) deflecting a distal section ofthe inner catheter about a transverse axis to position themultiple-needle electrode near a target on an interior wall of the heartchamber; (c) intimately contacting the electrode with an intracardiactissue; and (d) applying RF energy for ablation.
 2. A method foroperating an ablation catheter as in claim 1, wherein a distance of theneedles of said additional multiple-needle electrode is 2 mm or less.